[PATCH v5 3/3] drm/xe: Add WA BB to capture active context utilization

[Tvrtko Ursulin]

Hi,

One question below in the context of the missing workarounds series I am 
working on:

On 09/05/2025 17:12, Umesh Nerlige Ramappa wrote:

8><

> +#define CONTEXT_ACTIVE 1ULL
> +static void xe_lrc_setup_utilization(struct xe_lrc *lrc)
> +{
> +	u32 *cmd;
> +
> +	cmd = lrc->bb_per_ctx_bo->vmap.vaddr;
> +
> +	*cmd++ = MI_STORE_REGISTER_MEM | MI_SRM_USE_GGTT | MI_SRM_ADD_CS_OFFSET;
> +	*cmd++ = ENGINE_ID(0).addr;
> +	*cmd++ = __xe_lrc_engine_id_ggtt_addr(lrc);
> +	*cmd++ = 0;
> +
> +	*cmd++ = MI_STORE_DATA_IMM | MI_SDI_GGTT | MI_SDI_NUM_DW(1);
> +	*cmd++ = __xe_lrc_ctx_timestamp_ggtt_addr(lrc);
> +	*cmd++ = 0;
> +	*cmd++ = lower_32_bits(CONTEXT_ACTIVE);
> +
> +	if (lrc_to_xe(lrc)->info.has_64bit_timestamp) {
> +		*cmd++ = MI_STORE_DATA_IMM | MI_SDI_GGTT | MI_SDI_NUM_DW(1);
> +		*cmd++ = __xe_lrc_ctx_timestamp_udw_ggtt_addr(lrc);
> +		*cmd++ = 0;
> +		*cmd++ = upper_32_bits(CONTEXT_ACTIVE);
> +	}
> +
> +	*cmd++ = MI_BATCH_BUFFER_END;

Matt Roper raised the suggestion in another series that we should always 
use the iosys helpers for writing into mapped BOs. Later I realised this 
code uses the same shortcut as I did. I probably even lifted the concept 
since I placed my function right next to this one. :)

So question is what is the definitive recommended way to write into 
mapped BOs? Is the direct writes shortcut acceptable, or this also needs 
changing?

> +
> +	xe_lrc_write_ctx_reg(lrc, CTX_BB_PER_CTX_PTR,
> +			     xe_bo_ggtt_addr(lrc->bb_per_ctx_bo) | 1);

Btw here code uses the iosys helpers. It is a different BO but they are 
created/mapped the same AFAICT.

Regards,

Tvrtko